In furnaces having multiple rows of burners, such as reforming furnaces or reformers, burners positioned in close proximity to walls and/or corners of the furnace perform differently than burners positioned distal from walls and/or corners of the furnace. Generally, in comparison to burners positioned distal from the walls and/or corners of the furnace, burners positioned in close proximity to walls and/or corners of the furnace interact with the wall of the furnace more and produce greater amounts of NOx.
Great Britain patent GB2071832, which is hereby incorporated by reference in its entirety, discloses a furnace and the operation thereof. Specifically, the GB2071832 patent discloses furnace level air staging in a boiler. Generally, the burners in the boiler are provided with combustion air that is much less than stoichiometric (about 60% to about 80% of stoichiometric), and the remaining combustion air is provided by ports in the furnace away from the boilers. To promote flame stability, some of the burners are provided with combustion air that is stoichiometric in order to stabilize surrounding flames. For example, burners positioned at the end of a row can be provided with combustion air being up to 100% stoichiometric. Providing the burners positioned at the end of the row with combustion air that is 100% stoichiometric increases the flame temperature proximal to the burners at the end of the row. Such increase in temperature results in more heat interacting with the wall of the furnace, thereby producing more nitrogen oxides (NOx).
U.S. Pat. No. 4,454,839, which is hereby incorporated by reference in its entirety, discloses a furnace. Specifically, the U.S. Pat. No. 4,454,839 discloses a burner arrangement and flame orientation to control gas currents within an ethylene cracker. The U.S. Pat. No. 4,454,839 discloses using an aerodynamic pattern associated with combustion gases to achieve a stable flame pattern, decreased flame impingement on process tubes, and increased mixing. Being related to an ethylene cracker, which includes all burners being positioned close to walls, the U.S. Pat. No. 4,454,839 fails to disclose any distinction between burners proximal to walls and burners distal from walls.
U.S. Pat. No. 5,690,039, which is hereby incorporated by reference in its entirety, discloses a method and apparatus for reducing the production of NOx using spatially selective cooling. In the U.S. Pat. No. 5,690,039, a cooling fluid is used to selectively cool regions of high NOx generation, thereby reducing NOx generation. Use of the cooling fluid results in capital expense associated equipment providing the cooling fluid and associated with including the appropriate configurations for the furnace. Also, using the cooling fluid reduces efficiency by reducing the percent of the total heat produced from the fuel combustion that is absorbed by the process.
What is needed is a method and combustion system generating low NOx emissions having low capital expenses, high efficiency, and/or low furnace-burner interaction.